The present invention relates to a method of manufacturing a connecting rod for coupling the piston and the crankshaft of an automotive reciprocal engine such as a gasoline engine.
Hot-forged medium carbon steel has been used as a material for a conventional connecting rod. In recent years, however, a high-strength sintered material has come to be used for purposes of reducing the machining steps and the machining margin.
Japanese Patent Laid-Open No. 63-128102, for example, discloses a method of manufacturing a sintered connecting rod, in which a provisional formed body of a bearing section made of bearing metal powder is assembled on a provisional formed body of the connecting rod of metal powder, and the resulting assembly is forged or sintered thereby to produce a sintered connecting rod integrated with the bearing section.
The above-mentioned conventional sintered connecting rod, in which the bearing section is integrated with the connecting rod body, can be easily assembled on the crankshaft. In view of the fact that the sintering or forging step is performed after a provisional formed body of the bearing section is assembled on a provisional formed body of the connecting rod, however, the two provisional formed members cannot be easily set in position relative to each other in the course of manufacture, and an increased number of manufacturing steps is required. Also, the low adherence between the connecting rod body and the bearing section makes it difficult to transfer the heat of the bearing section, thereby leading to the problem of the bearing section being easily overheated. These problems of the connecting rod remain unsolved.